Permanent magnet and method of making it



Patented Feb. 13, 1934 1 UNITED STATES PATENT OFFICE 1,941,274 vPERMANENT moms-r AND ua'rnon or MAKING rr William E. Ruder, Schenectady,N. 2., assignor to General Electric Company, a corporation of New YorkNo Drawing. Application Februaryl, 1933 Serial No. 654.764

6 Claims. (Cl. 1'I521) The present invention relates to magneticmaemployed. For example, when the casting is terial and moreparticularly to cast alloy permaheated to a temperature of 600 C. theheatin nent magnets and to a method of making them. period may be aboutfive hours, while for a tem- It is one of the objects of the presentinvention perature of 650 C. the same results may be 5 to provide apermanent magnet, composed of obtained in about half an hour. Theproduct so relatively cheap materials, which may be fabriobtained afterheating the casting in the 600 to bated easily and cheaply and which hasdesirable 700 C. temperature range etches entirely diil'ermagneticqualities. ,ent from the product obtained after heating the The novelfeatures which are characteristic of casting at about 1000 C. Theexplanation of 1 my invention are set forth with particularity in thisis that heating in the 600 to 700 0. range the appended claims. Myinvention however will affects precipitation of an age hardening combestbe understood from reference to the followpound in thecasting. Thishardening compound ing specification. is composed of particles ofsub-microscopic size.

My improved magnet material generally con- I have obtained the mostsatisfactory results 15 sists of a mixture of iron, nickel and aluminumwith alloys consisting of 10 to 12% aluminum, 7 in which the iron maycomprise from about 60% about 20% nickel and the remainder iron. Age to70% of the composition, the aluminum from hardened alloys of thiscomposition have a coabout 6% to about 15% and the nickel from aboutercive force varying from about 330 to 350 gilto about 30%. Theingredients of the alloy berts per centimeter, a residual varying from20 in desired proportions are melted in any suitable about 7100 to 8500gauss, and a maximum energy 7 furnace and then poured into castings. Toobor BHmBX. varying from about one to one and tain the most satisfactorymagnetic qualities in one-half million. For the same maximum enthe alloythe casting preferably should be cooled ergy the relation of thecoercive and residual may from the liquid to the molten condition verybe varied with variations of the heat treatment 5 quickly. This may beaccomplished by casting and composition. For example, a composition themetal in a chill mold. If desired, however, 2. containing nickel gives alower residual, sand mold may-be employed. Under the latter other thingsbeing equal, and a higher coercive circumstances it will be founddesirable to sprinforce than a composition containing 20% nickel, klewater on the mold immediately after the castwhile prolonging the time orincreasing the teming has been poured and to pull the casting outperature of the treatment, increases the residual 5 of the mold as soonas it has solidified sufliciently andreduces the coercive force. topermit such action. If desired, the cover of If the cross section of thecasting is very small, the sand mold may be removed and the casting forexample x it will be found that its exposed to a strong air blast.magnetic qualities in the cast condition are about Since difference insize and necessary variaas good as the magnetic properties of largercast- 0 tions in casting conditions for various shapes ings which havebeen age hardened according to makes it difiicult to get uniform resultson all my improved process. However, although castmagnets of the samecompositiomit will generalings of very small cross sections havedesirable 1y be found desirable to give the alloy a heat magneticqualities in the as cast condition, it

treatment after the casting operation to obtain will nevertheless befound desirable to age harden 5 uniform results. This may c mpriseheating the all castings. This will be apparent when it is casting at anormalizing temperature in the considered that castings having a crosssection neighborhood of 1000 to 1500 C. This is merely of x are improvedby the aging process.

a corrective h treatment and is u l y 41- In general, the magneticqualities of castings of 45 plied until the e tir Castlng s heated tothe relatively small cross section are better than the normalizingtemperature- After h r a m nt magnetic qualities of castings ofrelatively large he casting is r p Cooled Preferably in cross section.This is apparently due to the ing air or oil. When the casting has beencooled rapidity t which t small castings solidity to the desired extent,i. e. about room temperafrom t hquid t t 5 -ture usually or to thetemperature of retreatment, While I prefer to employ only iron, nickeland it is given a further heat treatment which comaluminum as theingredients of my improved prises he in h ing to a temperature bealloythe presence of minor impurities does not tween about 600 C. and 700 Q.The time at materially affect the magnetic properties of the which thecasting is held in this temperature alloy. If desired, a few per cent ofchromium,

55 range may vary according to the temperature for example about 3 to5%, may be present in the alloy. However, the presence of chromium isnot desirable since it does not improve the magnetic properties of thealloy and does in= crease its cost. 1

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. An age hardened magnet consisting substantially of about 6% toaluminum, about to 30% nickel with the remainder iron.

2. An age hardened magnet consisting substantially of 10% to 12%aluminum, 20% to nickel with the remainder iron. I

3. An age hardened permanent magnet con sisting of about 10% aluminum,about 20% nickel and about 70% iron.

4. The method of making a permanent magnet cast alloy consistingsubstantially of about 6% to 15% aluminum, about 20% to nickel, and theremainder iron, which comprises melting the ingredients of the alloy,casting the alloy, quickly cooling the alloy from the liquid to thesolid state and aging the alloy at a temperature varying from about 600to 700 C.

meagre 5. The method of making a permanent magnet cast alloy consistingsubstantially of about 6% to 15% aluminum, about 20% to 30% nickel, andthe remainder iron which comprises melting the ingredients, casttng thealloy. quickly cooling the alloy from the liquid to the solid state,heating the casting at a temperature between 1000 C. and 1500" C. andcooling and then heating the casting at a temperature below 1000 C. buthigh enough to cause precipitation hardness thereof.

6. The method of making a permanent magnet cast alloy consisting ofabout 6% to 15% aluminum, about 20% to 30% nickel and the remainder ironwhich comprises melting the ingredients of the alloy, casting the alloy,quickly cooling the alloy from the liquid to the solid state and agingthe casting at a temperature below 1000 C. but high enough to causeprecipitation hardness of the alloy.

WILLIAM E. RUDER.

